The Lajnah ad-Da’imah stated:

أما الوليمة أو الاحتفال بمناسبة ختم القرآن فلم يعرف عنه صلى الله عليه وسلم ولا عن أحد من الخلفاء الراشدين رضي الله عنهم ولو فعلوه لنقل إلينا كسائر أحكام الشريعة، فكانت الوليمة أو الاحتفال من أجل ختم القرآن بدعة محدثة

As to the banquet of completing the Qur’an, the Prophet (peace be upon him) and the Rightly Guided Caliphs (may Allah be pleased with them) are not known to have prepared any banquets for such an occasion. Had they practiced this custom, it would have been handed down to us like all other rulings of Shari`ah. Consequently, this practice is considered an act of Bid`ah (innovation in religion).

[Reference]

Mentioned by

AbdulFattaah Bin Uthman
Abu Fajr